The present disclosure is related to radiation sensors, and more specifically to such sensors formed on a flexible substrate.
Conventional large-area thin-film sensors comprise an array of addressable pixels covered by a continuous layer of radiation-sensitive material. The radiation-sensitive material typically generates photons in the region in which radiation (e.g., x-rays) is incident thereon. These photons are converted into a charge and delivered to pixel(s) below the point of incidence of the radiation. The charge may then be read out from each pixel, and the extent and location of the incidence of radiation thereby determined. One example of such a sensor may be found in U.S. Pat. No. 5,619,033, which is herein incorporated by reference.
Typically, sensor arrays and the overlying sensor layer are formed on a rigid substrate such as glass. However, increasingly there is a desire for such sensor arrays to be provided on a flexible substrate such as sheet plastic. When formed on a flexible substrate, conformal sensor arrays may then be provided. However, there are a number of manufacturing challenges when forming devices on flexible substrates, particularly plastics. One such challenge is the thermal expansion coefficient mismatch between the plastic substrate and the materials deposited thereon. The difficulties introduced by this mismatch significantly increase as the thickness of the layer(s) deposited on the substrate increase.
For example, while typical thin-film transistor (TFT) stacks are quite thin, typical radiation sensor layers are relatively very thick, on the order of 1 μm (micrometer) or more in thickness. When fabricated over a plastic substrate, this relatively thick layer exhibits cracking and delamination due to the difference in thermally-induced expansion and contraction between the plastic substrate and the sensor layer material. This cracking and delamination results in poor device performance and high rates of device failure.
Therefore, there is a need in the art for a method of producing a radiation sensor structure on a flexible substrate with improved accommodation for the thermal mismatch between the substrate and the sensor structure materials and processes. More particularly, there is a need in the art for a structure and method of producing that structure consistent with the materials and processing steps currently used to produced sensor devices yet is significantly more tolerant of the thermal mismatch between substrate and sensor layer than current structures and methods for producing them.